Patent GB-875578-A (GB)
Title: Improvements in or relating to character recognition systems
IPC: G06V10/10
Filed: 1960-03-31
Abstract: 875,578. Automatic character reading. WESTERN ELECTRIC CO. Inc. March 31, 1960- [April 14, 1959], No. 11384/60. Class 106 (1). In a character recognition apparatus the characters are sensed in motion by two radial scanning patterns as shown in in Fig. 3 the two patterns being centred on upper and lower guide lines lb, 1c over which the characters are printed or written as in Fig. 1. The scanning patterns are traced on the screen of a cathode-ray tube FSS, Fig. 4, and projected by a lens SL on to the document to be read. The guide lines are in one colour and the characters in another and filters FLR, FLC for these two colours pass the reflected light to corresponding photo-multiplier tubes PMR, PMC. The former is used to centre the radial patterns on the two guide lines and the latter produces signals when the character is sensed during a scan. Only signals obtained in selected segments are allowed to pass to the recognition circuitry, these being shown shaded in Fig. 5. Radial scans start centred on the upper line lb and progress in an anti-clockwise direction. During scans 24-31 the photomultiplier PMC is connected to the recognition circuitry to provide the sensing area a. Other areas b, c and d are provided in the same way and after scan 127 the centre moves to the lower line for a further series of radial scans giving sensing areas e, f, g and h. The gates are controlled by a counter receiving clock pulses, the stages of which are gated together so that one gate gives an output for counts 24 to 31 another for counts 72-79 and so on. The clock pulses are also used to initiate the radial scans, being passed to a saw-tooth voltage generator, each pulse triggering the generator to produce the saw-tooth voltage. For each of the two scan patterns a sine wave generator is triggered by a signal from the clock pulse to produce 360 degrees of sine wave. This wave and the saw-tooth wave are applied to a modulator and the resulting signal, a sawtooth voltage modulated by a sine wave voltage is applied to one of the deflection coil (or plate) of the flying spot scanner. This modulated signal is also applied to a 90 degrees phase shifter and the output applied to the other deflection coil. By this means each group of 128 clock pulses produces 128 radial scans of the character. The two different centres are located by a standing bias voltage applied to the vertical deflection coil which for one centre is connected in series with a resistance and for the other is connected directly. The resistance is cut out by a gate energized by the highest stage of the clock pulse counter during counts from 128 to 255. Signals derived from the photo-multiplier PMC when the radial scan line crosses a part of the character are amplified and clipped at 804, Fig. 8, and used to set a flipflop 805 which is reset at the end of the scanning line by the corresponding clock pulse delayed at 800. The output of the flip-flop, on resetting is applied to a binary counter BC2. One and only one signal is counted for each radial scan line if a character is intersected. The number of intersections is unimportant. The counter has four binary stages, outputs of which are gated together in And gates 806-808 and Or gate 809 to give an output if six, seven or eight of the adjacent radial scans of a particular area (a, b, c, &c., Fig. 5) intersect a character. If dirt or a spurious mark on the paper is sensed, only two or three scans cross it and the Or gate 809 according gives no output but a true mark being intersected by six or more scans and an output is obtained on " mark present " lead MP. Where no true mark is present an inverter produces an output on lead NMP. The counter BC2 is reset at the end of each scan area. The signals on lead MP are gated as mentioned above in even-numbered gates 812 to 826 to extract on separate leads signals relating to sensing areas a, b, c &c. and they are applied to the corresponding threestage binary counters BC3a, BC3b, BC3c, &c. The character is sensed in motion and as it passes through the scanning position it is sensed a number of times, e.g. twenty times by the scanning pattern. Lines of the character lying along the length of a sensing area, e.g. the line of numeral "1" relative to areas a, c and h pass through these areas quickly during movement of the character and are detected in a fewer number of scanning patterns than lines at right-angles. Lines parallel to sensing areas are to be ignored in the recognition circuitry and this is effected by the counters BC3a &c. which require a count of eight before passing a signal to lead a1 &c., that is no output is produced unless a line is detected in eight successive scans. The "no mark present" signals on lead NMP is applied to And gate 830 with a delayed end of scan area signal and passes through the odd-numbered gates 811-825 to reset the counters BC3a &c. when a blank scan is detected. The outputs from the counters accordingly represent the detection of a line by a scanning area in at least eight consecutive scans. If this condition is absent inverters 827 produce signals on leads a0 &c. Recognition.-The recognition circuitry is designed to respond to predetermined logic code for each numeral or letter. In each of three successive stages in the sensing of a particular numeral (say) a full line would be expected in certain sensing areas and lines would not be expected in other sensing areas. In further areas lines might or might not be detected and the circuit ignores these. As an example the numeral "1" may be considered. The two scanning patterns are treated separately, the top one first. As the characters move from right to left under the sensing pattern in the first stage the area d only will intersect the numeral. Accordingly there should be a d1 signal, an a0 and a c0. The area b may still be detected the previous character and is ignored. The leads d1, a0 and c0 are gated together in And gate 1001, Fig. 10, and the output used to set flip-flop 1002. Later in the scanning process the numeral lies over areas a and c but as described above, these do not respond since the time of detection is too short. The second test is therefore that signals a1 c1 do not exist. These leads are accordingly applied via Or gate 1003 to And gate 1004 which has a second input from flip-flop 1002. If a crossing line, i.e. a horizontal line is detected by either of areas a and c and flip-flop 1002 is set the And gate 1004 gives an output which sets flip-flop 1005 which removes the enabling signal on And gate 1006. The third stage of sensing should detect a line in area b and none in areas a and c. Area d may now be detecting the next character and is ignored. Lines a0, b1 and c0 are applied to gate 1006 to set flip-flop 1007. The lower part of the sensing pattern uses similar combinations of signals at the three stages from areas e, #, g and h to set flip-flop 1014. The outputs from the upper and lower flip-flops are gated together in And gate 1008 and give an output on the " 1" lead if the necessary conditions are fulfilled. Closed loop resolution.-Confusion may arise between numerals " 4 " and " 9 " and these are distinguished by an extra circuit which detects the presence of a closed loop and counts the number of corners in the loop. A " 4 " is distinguished by having three corners in its loop as opposed to one or none in the loop of the nine. As shown in Figs. 17A, 17B a signal is derived for each radial scan which is proportional to the distance of the line of the loop from the centre of the scanning lines. For a circle the envelope of these signals will be in the form of a smooth curve but an angled shape such as a triangle will produce an envelope with cusps, one for each angle. The presence of a closed loop in the upper part of the sensing pattern is detected by the circuit of Fig. 13 consisting of a gate 1303 receiving lines a1, b1, c1 and d1. When each area detects a crossing line a closed loop can be presumed and gate 1303 sets flip-flop 1304. A signal is thereby applied to an input of And gate 1305 and to the control input of gate 1307. The clipped signals from the photo-multiplifier tube PMC, Fig. 8, pass on line THO to gate 1307. The time of appearance of a signal in each scan gives the distance of the loop from the centre of the scan. These signals passing through gate 1307 are applied to gate 1320 to which is applied the saw tooth voltage of the scanner control. The output from gate 1320 is in the form of a pulse the amplitude of which represents the time of arrival of the sensing pulse in each radial scan, i.e. the distance of the loop from the centre at each of 128 points. A band-pass filter 1321 of which the frequency is set, say at three times the scan repetition frequency, will respond to a triangular loop because of the three cusps or discontinuities in the envelope of the output pulses from gate 1320. The filter signal via an amplifier 1323 and a threshold device 1324 sets a flip-flop 1312 which by enabling gates 1309 or 1310 distinguishes between the numerals " 4 " and "9." Similar circuits may be used to distinguish between other similar characters, e.g. "D" and "O." The signals from the recognition circuits are applied to utilization equipment such as a punch or magnetic tape apparatus. A signal on any character lead serves also to reset the centre circuitry ready for the next character. The number of scanning cycles before a recognition signal appears is counted and an alarm given if the number of cycles is too low or too high. Automatic scan registry.-The registration photo-multiplier PMR which as previously described is used to keep the scanning centres on the upper and lower guide lines lb, lc, Fig. 3. In proper registration the area a will detect line la only and area h will detect only line ld. Any error will cause one area to sense two lines and the other to sense one, and a worse error will cause one area to intersect one